1. Field of the Invention
This invention relates to a pressure cylinder such as a master cylinder, primarily for use in a vehicle brake or clutch hydraulic system, and particularly to such a cylinder molded from plastics material and having an integral mounting flange.
2. Description of the Prior Art
Because the mounting flange of such a cylinder is usually of significantly greater thickness than the cylinder wall, differential contractions can occur upon cooling after molding of the cylinder, resulting in cylinder bore distortion in the region of the flange. Such distortion can create problems in maintaining an adequate seal between the cylinder internal wall and an internal co-operating piston assembly and can also result in the snagging of the piston and/or its associated seals and possible consequent jamming of the piston assembly within the cylinder.
One attempt to solve this problem consists in mounting the flange by way of an outer cylindrical formation generally co-axial with the surrounding the cylinder proper, the formation being connected to the cylinder at a position beyond the inward limit of piston travel. This arrangement removes any bore distortion resulting from the flange molding to a location at which it does not significantly adversely affect the travel or sealing of the piston assembly. However, a disadvantage of this arrangement is that the overall bulk of the cylinder and consequent installation space required is significantly increased, as are material costs. Moreover, the arrangement can be unacceptable when the mounting flange is required to be adjacent the open cylinder end because the cylindrical portion then required can be excessively long, leading to the possibility of untoward flexing of the cylindrical formation, and consequent movement of the cylinder taking place during operation of the master cylinder.